Largely die to no really amazing news about WoW. People hate the current expansion with a passion and a few tweaks have been made; but not enough to really fix it. There are a ton of comments I've read with players saying they will never level an alt through that content. If people only have a single character at max level they're more likely to just quit out of boredom. Classic will have a bit of a life, but an MMO with zero new content ever added will die off fairly quickly.

This time around was them boasting about the past and nothing to really show for the future.